Antennas function to receive and transmit free-space electromagnetic waves. When an antenna is receiving, the antenna transforms free-space propagating waves by inducing a guided electromagnetic wave within the antenna. The guided electromagnetic wave is then fed into an integrated circuit. The integrated circuit then deciphers the signal being transmitted. When an antenna is transmitting, the antenna receives the guided electromagnetic wave for transmission from a feed line and induces an electric field surrounding the antenna to form a free-space propagating electromagnetic wave.
An important consideration in the selection and design of the antenna is the propagation pattern of the free-space propagating electromagnetic wave. In a typical application, a transmitting antenna needs to be able to transmit a guided electromagnetic wave to and from another antenna located on a device such as a base station, hub, or satellite. The base station can be located in any number of directions from the transmitting antenna. Consequently, it is essential that the antennas for such wireless communication devices have an electromagnetic propagation pattern that radiates in all directions.
Another important factor to be considered in designing antennas for wireless communication devices is bandwidth of the antennas. Wireless communication devices such as cellular phones and personal data assistants (PDAs) operate over a frequency band of approximately 1.85–1.99 Gigahertz, thus requiring a useful bandwidth of 7.29 percent. Antennas need to operate at the specific bandwidth of the wireless device. Accordingly, antennas for use on these types of wireless communication devices are be designed to meet the appropriate bandwidth requirements, otherwise communication signals will be severely attenuated.
The demand for compact and inexpensive antennas has increased as wireless communication has become commonplace in a variety of applications. Personal wireless communication devices, for example, cellular phones and PDA have created an increased demand for compact antennas. The increase in satellite communication has also increased the demand for antennas that are compact and provide reliable transmission. In addition, the expansion of wireless local area networks at home and work has also necessitated the demand for antennas that are compact and inexpensive.
A microstrip patch antenna is a type of antenna that offers a low profile, i.e. thin, and easy manufacturability, which provides a great advantage over traditional antennas. FIG. 1 shows a perspective view of a general shorted-wall, quarter-wave microstrip patch antenna 100. The patch antenna 100 comprises a grounding plate 102, a patch plate 104, and a shorting wall 106. A coaxial cable 108 supplies the guided electromagnetic wave that will be transmitted. Typically the coaxial cable 108 is a 50-ohm cable comprising a signal wire and a ground wire. The signal wire carries the guided electromagnetic wave. The ground wire connects to the ground plate 102 of the microstrip patch antenna 100. The signal wire or feed line 110 passes through an aperture 114 in the ground plate 102 and connects at a location on the patch plate 104. The free-space electromagnetic wave is induced by the patch plate 104 causing a free-space electromagnetic wave to propagate from the patch plate 104.
A properly designed antenna should have a reactive impedance component equal to zero and have a real impedance component equal to a load impedance of the antenna. Additional techniques that allow an antenna designer to manipulate the real impedance of the antenna can provide better designs for patch antennas. Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.